The Difference between Air-Leakage & Ventilation

VentilationVentilation is the active process of “changing” or replacing air to regulate temperature and moisture. It should always occur under controlled conditions, by opening windows or with ceiling or exhaust fans. If you are building a highly energy efficient and air-tight home, then a mechanical ventilation system or heat recovery unit gets really important.

Ventilation should NEVER happen through gaps and air-leakage. Ventilation is important to support the ability of thermal mass to absorb and release heat in order to regulate the indoor temperature.

It is necessary to ascertain where natural breezes are to locate the windows accordingly. Landscaping and other buildings can influence and obstruct air flow; therefore it is necessary to visit and check the site before locating windows. Cool summer breezes in and around Melbourne usually come from south; detailed information can be found from the Bureau of Meteorology (BOM) web site.The less gaps and air-leakage occur the air-tighter a building gets. Therefore regular ventilation is mandatory to renew oxygen and discharge odours, water vapour, carbon dioxide and other contaminations.

For instance, in Germany it’s recommended to cross-ventilate every day for a few minutes, even in winter. If the occupants forget to ventilate regularly, water vapour will be trapped inside and will lead to mildew and mould on the walls and the ceilings.

If you are building a really air-thight house it will most likely not be possible to manually ventilate the house sufficiently, which could lead to moisture and potentially mould build up inside the house. Therefore, the more energy efficient your home is, the more important mechanical ventilation gets…

Cross-ventilationOpenable windows and external doors should be located on different sides of the home, with less than 8 metres distance between them to allow for adequate and effective air flow. Cooler air enters the building where the breeze is loctated, passes through the building and exits on the other side. The warm air inside gets replaced by fresh and cooler air.

On the other hand, if you are installing a mechanical ventilation or heat recovery system this system will look after the ventialtion and cross ventilation for you.

I know, it can be a bit confusing right?

To summarise a bit: When you have a ‘normal’ house or an energy efficient passive solar designed home ventilation and cross ventilation is really important to regulate the indoor climate and windows and doors have to be designed accordingly.

Whereas if you are designing a home according to the strict passive house design guidelines the window and door locations are not as important anymore, as the mechanical system will look after the ventilation.